Basically - it's a balance - don't be too dumb, but don't be too clever either. I'd submit Python as being solidly in the middle ground here.
Your average PHP web dev is not the cutoff for the 95th percentile. But yes, I can imagine them trying to understand monads. I have also observed them succeeding at understanding monads. They aren't hard to learn, just something you need to learn. Being able to learn simple things doesn't make you the top 5%.